[T]he primary difference between the two species is cold tolerance: A. pigra can and does live at higher altitudes than A. palliata, ranging high enough that it must tolerate freezing temperatures…Larger monkeys with larger, more complex molars, differences in throat anatomy, and greater cold tolerance, in contrast to a smaller, more cosmopolitan species, with the opportunity for gene flow during interglacials. They sound like Neanderhowlers.